1. Field of the Invention
This invention relates to a refractory flame-gunning apparatus that is used for the repair of furnace walls, inside walls of molten-metal containers and the like by spraying refractories onto their surface through a gas flame. More particularly, this invention relates to a flame-gunning apparatus that feeds refractory powder into a flame produced by burning a mixture of inflammable and combustion-assisting gases, thereby melting the refractory powder and applying the molten refractory onto the surface to be coated, and also to an apparatus that instantaneously stops any backfire that occurs in the inflammable and combustion-assisting gas supplying system of the refractory flame-gunning apparatus.
2. Description of the Prior Art
This type of flame-gunning apparatus has a flame-gunning burner comprising a plurality of refractory powder projecting nozzles and flame projecting nozzles. The flame-gunning burner shoots refractory powder and flame together onto the wall surface requiring repairs. In this type of refractory flame-gunning apparatus that employs flame, backfire, a phenomenon in which flame runs backward from the flame nozzles into the gas supply passage, can occur. Backfire occurs when the inflammable gas ejected from the flame nozzles burns faster than the rate at which it is ejected. More specifically, backfire occurs, for example, when the gas ejection rate drops as a result of the clogging of the flame nozzles, when the combustion rate rises as a result of an increase in gas temperature, when the gas flow rate or pressure changes, or when the flame nozzles are hit or clogged as a result of the mishandling of the apparatus in transit.
Backfire can damage the inside of the flame-gunning burner, sometimes to such an extent that repairs can no longer be continued or a serious disaster results. When backfire occurs in a conventional apparatus, therefore, the operator stops the supply of the inflammable and combustion-assisting gases by closing the feed valves on the inflammable and combustion-assisting gas feed lines either manually or by remote control. However, it is difficult to stop the gas supply instantaneously by this type of action taken by the operator and, therefore, there is a likelihood that the backfire will lead to a serious disaster. It is of course ideal to thoroughly eliminate the possibility of backfire.
For example, the flame-gunning apparatus proposed in the Japan Examined Utility Model Publication No. 31332 of 1981 is designed to prevent the occurrence of backfire on termination of gunning. Still, such an apparatus can hardly achieve complete prevention of backfire since backfire results from various causes as described previously, even while gunning is being effected.
A safety device for a refractory flame-gunning apparatus disclosed in the U.S. Pat. No. 3,684,560 closes a valve in the oxygen feed pipe when a gas pressure irregularity in the lance is detected by a manometer. However, the feed valve cannot be closed the moment backfire occurs since the design is such that the valve does not close until a control device operates upon receiving a signal from the manometer. Besides, the reliability of the safety device is low since it does not function if any of the manometer, control device and feed valve breaks.
As a consequence, there has been a strong demand for the development of an apparatus that can instantaneously and surely stop a backfire.